A stroke is a sudden loss of brain function caused by a blockage of a blood vessel to the brain (ischemic stroke) or a rupture of a blood vessel to the brain (hemorrhagic stroke). Each year, more than 700,000 people in the U.S. alone suffer a new or recurrent stroke and the consequences can be devastating. Over 150,000 of these events end in death, and many of those who survive are left seriously and permanently impaired. During each minute of progression of a stroke, about two million brain cells die. Approximately fourteen billion brain cells die during the average ten-hour stroke. As such, the time from onset of a stroke to its diagnosis and treatment by medical personnel is critical.
Accordingly, it is highly desirable to provide techniques for detecting the onset of a cerebral stroke within a patient for promptly notifying family members, caregivers or emergency personnel. It is particularly desirable to detect stroke using an implantable medical device as many elderly patients prone to stroke already have such devices implanted therein or are candidates for such devices.
Useful techniques for detecting stroke using implantable medical devices are described in U.S. patent application Ser. No. 12/366,526, filed Feb. 5, 2009, to Park and entitled “Systems and Methods for use with an Implantable Medical Device for Detecting Stroke Based on Electrocardiac Signals,” and now U.S. Pat. No. 8,241,221, the disclosure of which is hereby incorporated by reference. Briefly, techniques are provided therein for detecting stroke within a patient based on predetermined changes in an electrocardiac signal, such as changes within an electrocardiogram (ECG) sensed by a subcutaneous monitor or changes within an intracardiac electrogram (IEGM) signals sensed by a pacemaker or ICD. Exemplary features indicative of possible stroke include the onset of prominent U-waves, the onset of notched T-waves, and changes in ST segment duration or QT duration or dynamic trends in these parameters. In one example, a preliminary detection of stroke is performed by an implantable device based on an analysis of features of the ECG or IEGM. The device transmits a signal indicative of possible stroke to a bedside monitor or other external system, which generates a stroke questionnaire for use in confirming the stroke. Family members or other caregivers input answers to the questionnaire into the external system, which confirms or disconfirms the stroke. Emergency personnel can be automatically notified.
It would be desirable to provide additional or alternative techniques for detecting stroke using an implantable medical device, particularly techniques wherein the stroke can be confirmed based on additional signals detected within the patient, rather than based on a questionnaire answered by family members or other caregivers. It is to this end that aspects of the present invention are directed. It is also desirable to provide techniques for distinguishing stroke from cardiac ischemia from one another based on signals sensed using an implantable medical device. In this regard, certain changes in electrocardiac signals caused by stroke (such as changes in ST segment duration and in QT duration observed within ECGs or IEGMs) can also be caused by cardiac ischemia and hence there is a need to reliably distinguish stroke from cardiac ischemia when using electrocardiac signals. (Note that cardiac ischemia is distinct from an ischemic stroke. Cardiac ischemia is an ischemia occurring within the heart that affects heart function. Ischemic stroke is an ischemia occurring within the brain that affects brain function.)